Measurements of the Imaginary Part of the Refractive Index Between 300 and 700 Nanometers for Mount St. Helens Ash

Patterson, E. M.

doi:10.1126/science.211.4484.836

Cited by 47 publications

(45 citation statements)

References 12 publications

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“…The amount of light scattered by a particle is defined not only by a particle's size but also by its shape, refractive index, n, (which may be complex in the case of light absorbing materials) and whether or not the particle is homogeneous. These additional variables are particularly important in atmospheric measurements where OPCs are often employed to measure many different particle types from spherical homogeneous waterdroplets (n = 1.33) to angular volcanic ash particles (n in the range 1.5 − 1.6 + 0.001i − 0.02i Muñoz et al, 2004;Patterson, 1981;Patterson et al, 1983).…”

Section: Optical Particle Countersmentioning

confidence: 99%

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

et al. 2012

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Section: Optical Particle Countersmentioning

confidence: 99%

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

et al. 2012

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“…Three different volcanic ash sources were used, providing a variety of mineral and thus, optical properties. Two wavelengthdependent indices of refraction of Mount St. Helens ash from the 18 May 1980 eruption were obtained from Patterson (1981). The first sample, collected in Boulder, Colorado corresponds to the first pulse of the eruption and is characterised by a dark grey colour and a high absorption coefficient in the visible wavelengths.…”

Section: Optical Properties Of Mineral Dust and Volcanic Ashmentioning

confidence: 99%

“…In the single-layer implementation of the model, SNICAR-online (Flanner et al, 2007), multiple snow types can be modelled by changing the snow grain radius. However, only a single type of volcanic ash derived from Patterson (1981) and combined mineral refractive indices as an approximation of mineral dust were used. Furthermore, SNICAR-online does not allow for calculations in sea ice.…”

Section: L Lamare Et Al: Mineral Aerosol Deposits On Sea Icementioning

confidence: 99%

The impact of atmospheric mineral aerosol deposition on the albedo of snow & sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

2016

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Abstract. Knowledge of the albedo of polar regions is crucial for understanding a range of climatic processes that have an impact on a global scale. Light-absorbing impurities in atmospheric aerosols deposited on snow and sea ice by aeolian transport absorb solar radiation, reducing albedo. Here, the effects of five mineral aerosol deposits reducing the albedo of polar snow and sea ice are considered. Calculations employing a coupled atmospheric and snow/sea ice radiativetransfer model (TUV-snow) show that the effects of mineral aerosol deposits are strongly dependent on the snow or sea ice type rather than the differences between the aerosol optical characteristics. The change in albedo between five different mineral aerosol deposits with refractive indices varying by a factor of 2 reaches a maximum of 0.0788, whereas the difference between cold polar snow and melting sea ice is 0.8893 for the same mineral loading. Surprisingly, the thickness of a surface layer of snow or sea ice loaded with the same mass ratio of mineral dust has little effect on albedo. On the contrary, the surface albedo of two snowpacks of equal depth, containing the same mineral aerosol mass ratio, is similar, whether the loading is uniformly distributed or concentrated in multiple layers, regardless of their position or spacing. The impact of mineral aerosol deposits is much larger on melting sea ice than on other types of snow and sea ice. Therefore, the higher input of shortwave radiation during the summer melt cycle associated with melting sea ice accelerates the melt process.

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“…The stratospheric aerosols resulting from explosive volcanic eruptions are of two general types: silicate ash, produced directly at the time of the explosion, and a sulfuric acid-water aerosol, produced as a result of gas-toparticle conversion processes. The ash usually consists of glassy and crystalline material, reflecting its origination from volcanic magma and minerals [Patterson, 1981;Patterson et al, 1983]. The sulfate aerosol consists of sulfuric acid droplets which form after an eruption with a timescale of about 1 month and substantially increase the aerosol optical thickness of the stratosphere after large explosive eruptions [Hofmann and Rosen, 1983;Deshler et al, 1992;Bhartia et al, 1993;Russell et al, 1996].…”

Section: Volcanic Aerosol Modelsmentioning

confidence: 99%

Ultraviolet optical model of volcanic clouds for remote sensing of ash and sulfur dioxide

Krotkov¹,

Krueger²,

Bhartia³

1997

J. Geophys. Res.

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Abstract. The total ozone mapping spectrometer (TOMS) instruments have detected every significant volcanic eruption from November 1978 to December 1994 on the Nimbus 7 and Meteor 3 satellites and since July 1996 on the new satellites, TOMS-Earth Probe and ADEOS. We apply a radiative transfer model to simulate the albedos of these fresh eruption clouds to study the limitations of the present algorithm which assumes an absorbing cloud above a scattering atmosphere. The conditions are found to be approximated when the total absorption optical depth is less than 2 (i.e., 100 Dobson units (DU) SO2 at 312 nm or 300 DU SO2 at 317 nm). The spectral dependence of the albedo of a nonabsorbing Rayleigh atmosphere can be specified by only two parameters which are uniquely different when ash or sulfate aerosols are present in the stratosphere. However, the interaction between ash scattering and SO 2 absorption within a volcanic cloud produces a nonlinear effect at strongly absorbing wavelengths that accounts for overestimation of sulfur dioxide in ash-laden volcanic clouds by the Krueger et al. [1995] algorithm. Correction of this error requires knowledge of the ash properties. A method for determining two of the ash parameters from the longer TOMS wavelengths is described. Given the altitude of the cloud, surface reflectivity, and an estimate of effective variance of the ash size distribution, the optical thickness and either the effective radius or the index of refraction can be deduced. The ash retrievals are also needed to evaluate the tephra/gas ratio of eruptions and to compare the ash properties of different volcanoes. IntroductionThe purposes of this paper are to describe an optical model of volcanic clouds at ultraviolet (UV) wavelengths, to describe the simulated albedos used to test retrieval algorithms, to study limitations of remote sensing of thick volcanic clouds, to examine the interaction between ash scattering and sulfur dioxide absorption within a volcanic cloud, and to show the possibility of measuring ash properties from space. The sulfur dioxide results in the various volcanic cloud papers are based on the algorithm described by Krueger et al. [1995] using the level-2 Nimbus 7 data and calibration available prior to 1995. This algorithm was tested under lowlatitude conditions with simulated volcanic cloud albedos and found to produce SO2 retrievals with errors less than _+10%. However, when ash is present in the volcanic cloud, the retrieval overestimated sulfur dioxide by 15-25% depending on the particle size and composition. Because of this unexpected Copyright 1997 by the American Geophysical Union. Paper number 97JD01690.0148-0227/97/97JD-01690509.00 relation between sulfur dioxide and ash we initiated a study of the optical properties of volcanic clouds. A proposed optical model which includes ozone and SO2 gas absorption and scattering by volcanic ash is described in this paper.Given the optical model of a volcanic plume, we solve the radiative transfer equation to obtain the albedo at the TOMS...

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Measurements of the Imaginary Part of the Refractive Index Between 300 and 700 Nanometers for Mount St. Helens Ash

Cited by 47 publications

References 12 publications

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

The impact of atmospheric mineral aerosol deposition on the albedo of snow & sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

Ultraviolet optical model of volcanic clouds for remote sensing of ash and sulfur dioxide

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Measurements of the Imaginary Part of the Refractive Index Between 300 and 700 Nanometers for Mount St. Helens Ash

Cited by 47 publications

References 12 publications

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

Particle sizing calibration with refractive index correction for light scattering optical particle counters and impacts upon PCASP and CDP data collected during the Fennec campaign

The impact of atmospheric mineral aerosol deposition on the albedo of snow &amp; sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?

Ultraviolet optical model of volcanic clouds for remote sensing of ash and sulfur dioxide

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The impact of atmospheric mineral aerosol deposition on the albedo of snow & sea ice: are snow and sea ice optical properties more important than mineral aerosol optical properties?